This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440

Byrd, R.C.

Carey, T.A.

Gaarde, C.

Goodman, C.D.

Horen, D.J.

Krofcheck, D.

Larsen, J.S.

McClelland, J.B.

Rapaport, J.

Rees, L.

Sugarbaker, E.

Taddeucci, T.N.

Van Heerden, I.J.

Wagner, A.J.

English

IUScholarWorks

CHARGE-EXCHANGE REACTIONS 
SPIN TRANSFER MEASUREMENTS FOR ( p , n )  REACTIONS AT INTERMEDIATE ENERGY 
T . N . ~ a d d e u c c i '  
Univ. of Maryland, Col lege  Park,  Maryland and Indiana  Un ive r s i t y  Cyclo t ron  F a c i l i t y ,  Bloomington, I nd i ana  47405 
C.D. Goodman, R.C. Byrd, and I . J .  Van ~ e e r d e n t  
I nd i ana  U n i v e r s i t y  Cyclo t ron  F a c i l i t y ,  Bloomington, I nd i ana  47405 
T.A. Carey, J.B. McClelland, L. Rees 
Los Alamos Na t i ona l  Labora tory ,  Los Alamos, New Mexico 87545 
D.J .  Horen 
Oak Ridge Na t i ona l  Labora tory ,  Oak Ridge, Tennessee 37830 
J.S. Larsen  and C. Gaarde 
N ie l s  Bohr I n s t i t u t e ,  Un ive r s i t y  of Copenhagen, DK-2100, Copenhagen, Denmark 
J .  Rapaport  
Ohio Un ive r s i t y ,  Athens,  Ohio 45701 
E. Sugarbaker,  D. Krofcheck,  A.J. Wagner 
Ohio S t a t e  Un ive r s i t y ,  Columbus, Ohio 43214 
. 
P o l a r i z a t i o n  t r a n s f e r  observables  i n  
in te rmedia te -energy  nucleon-nucleus s c a t t e r i n g  a r e  
r e c e i v i n g  much c u r r e n t  a t t e n t i o n .  These obse rvab l e s  
can a c t  a s  s e n s i t i v e  " f i l t e r s "  f o r  n u c l e a r  s t r u c t u r e  
s t u d i e s  and a l s o  s e r v e  a s  impor tan t  t e s t s  of r e a c t i o n  
mode 1s .  
I n  t h e  l a s t  two yea r s ,  measurements of t r a n s v e r s e  
p o l a r i z a t i o n  t r a n s f e r  i n  ( p ,  n )  r e a c t i o n s  have been 
c a r r i e d  out  a t  t h e  Ind i ana  U n i v e r s i t y  Cyclo t ron  
F a c i l i t y  (IUCF). These measurements have spanned 
t h e  bombarding energy  range from 80 MeV t o  160 MeV f o r  
- Ep = 120 M e V  
U S  
6 - @ = 0" 
1 
4 - 
2 - J 
0 - l I f f I  I " 
4 - 
50 40 30 20 10 0 
excitation energy Ex (MeV) 
a  v a r i e t y  of t a r g e t s .  The nucleus  9 0 ~ r  has  been t h e  
F igu re  1. S p e c t r a  of t h e  d i f f e r e n t i a l  c r o s s  s e c t i o n  
o b j e c t  of much s tudy ,  both exper imenta l  and and p o l a r i z a t i o n  t r a n s f  e r  c ro s s  s e c t i o n  f o r  O ~ r ( ~ , n )  
a t  120 MeV and 0 = 0". 
t h e o r e t i c a l ,  i n  connect ion  wi th  t h e  ques t i on  of 
s p i n - f l i p  s t r e n g t h  d i s t r i b u t i o n s .  t r a n s i t i o n ,  f o r  which DNN = 1, s t a n d s  up prominently i n  
Sp in  t r a n s f e r  r e s u l t s  f o r  9 0 ~ r ( p , n )  a t  160 MeV t h e  oDNN spectrum. The g i a n t  GT resonance and t h e  
have been d i s cus sed  i n  a  p r ev ious  r e p o r t  and i n  a  low-lying GT s t a t e s  both have nega t i ve  p o l a r i z a t i o n  
r e c e n t  pub l i c a t i on .3  During 1985 a d d i t i o n a l  d a t a  f o r  t r a n s f e r  c r o s s  s e c t i o n s  because of t h e  c h a r a c t e r i s t i c  
' O ~ r ( ~ , n )  a t  120 MeV were obta ined .  S p e c t r a  of t h e  new DNN = -1/3 s i g n a t u r e  f o r  1' t r a n s i t i o n s .  
r e s u l t s  a r e  shown i n  F igu re  1. The t op  ha l f  of t h i s  S p e c t r a  of t h e  s p i n - f l i p  c r o s s  s e c t i o n  asNN, t h e  
f i g u r e  is t h e  d i f f e r e n t i a l  c r o s s  s e c t i o n  o(OO,Ex) and non-sp in- f l ip  c r o s s  s e c t i o n  a(1-SNN), and DNN a r e  shown 
t h e  bottom ha l f  is t h e  p o l a r i z a t i o n  t r a n s f e r  c r o s s  i n  F igu re s  2 and 3. The d a t a  i n  t h e s e  f i g u r e s  have 
s e c t i o n  oDNN. The O+ + O+ i s o b a r i c  ana log  s t a t e  been s o r t e d  i n t o  b in s  of 1 MeV width t o  reduce 
L T 4 
- E, = 160 MeV - 
4 :  e = o O  'I - 
- 1 - .  
- 
- 
- GT 
50 40 30 20 10 0 
excitation eneray Ex (MeV) 
6 - 1 1 1 1 1 1 1 I I I r '  
- E, = 120 MeV - 
50 40 30 20 10 0 
excitation energy Ex (MeV) 
Figu re  2. Sp in - f l i p  c r o s s  s e c t i o n  ( t o p ) ,  F igu re  3. Spin-f l i p  c r o s s  s e c t i o n ,  non-spin-f l i p  c r o s s  
non-s i n - f l i p  c r o s s  s e c t i o n  (middle) ,  and D m  (bottom) s e c t i o n ,  and Dm f o r  9 0 ~ r ( p , n )  a t  160 MeV and 0". 
f o r  99Zr(p ,n)  a t  120 MeV and 0'. 
s t a t i s t i c a l  s c a t t e r .  Some i n t e r e s t i n g  f e a t u r e s  emerge. about which t h e  g i a n t  i s o v e c t o r  d ipo l e  resonance is  
I n  p a r t i c u l a r ,  t h e  DNN spectrum a t  160 MeV r e v e a l s  a  cen t e r ed .  The p o l a r i z a t i o n  t r a n s f e r  measurements 
sequence of regions  where n a t u r a l  p a r i t y  and unna tu ra l  i n d i c a t e  t h a t  a  l a r g e  f r a c t i o n  of t he  s t r e n g t h  observed 
p a r i t y  e x c i t a t i o n s  a r e  a l t e r n a t e l y  most impor tant .  i n  t h i s  region  a t  0' has n a t u r a l  p a r i t y .  This  r e s u l t  
The observed va lues  of D N ~  f o r  t h e  region  of t he  i s  a t  odds wi th  r ecen t  c a l c u l a t i o n s  by O s t e r f e l d ,  Cha, 
g i a n t  GT resonance a r e  c l o s e  t o  t h e  nominal va lue  of and ~ ~ e t h , ~  who p r e d i c t  very l i t t l e  n a t u r a l  p a r i t y  
-113 expected  f o r  pure GT e x c i t a t i o n s .  The p re sen t  s t r e n g t h  a t  0' f o r  Ep = 200 MeV. The l o c a t i o n  of 
d a t a  cannot exclude t h e  p o s s i b i l i t y  of o t h e r  unna tu ra l  n a t u r a l  p a r i t y  s t r e n g t h  i n d i c a t e d  by t he  p r e sen t  
p a r i t y  e x c i t a t i o n s  i n  t h i s  region .  However, t h e  r e s u l t s  is i n  good agreement wi th  low energy 
exper imenta l  r e s u l t s  a r e  c o n s i s t e n t  wi th  t h e o r e t i c a l  measurements which a r e  most s e n s i t i v e  t o  t h e  AS=O 
p r e a i c t i o n s  t h a t  most of t h e  c ro s s  s e c t i o n  i n  t h i s  component of t he  1' resonance.  
r eg ion  corresponds  t o  GT e x c i t a t i o n s .  It is i n t e r e s t i n g  t o  compare t h e  t r e n d  i n  DNN i n  
The va lue  of DNN observed nea r  Ex = 20 MeV is  t h e  h igh- ly ing  continuum (Ex > 25 MeV) f o r  t h e  two 
p a r t i c u l a r l y  noteworthy. This  is the  e x c i t a t i o n  energy bombarding ene rg i e s .  The a l t e r n a t i n g  r eg ions  of 
n a t u r a l  p a r i t y  and u n n a t u r a l  p a r i t y  s t r e n g t h  seen  a t  
160 MeV a r e  no longer  ev iden t  a t  120 MeV. It i s  not 
y e t  c l e a r  whether t h i s  d i f f e r e n c e  can be a t t r i b u t e d  t o  
changes i n  t h e  e f f e c t i v e  i n t e r a c t i o n  a s  a  func t ion  of 
energy and momentum t r a n s f e r  o r  whether i t  i s  evidence 
f o r  o t h e r  r e a c t i o n  mechanisms becoming impor tant  a t  t h e  
lower ene rg i e s .  For example, a t  120 MeV t h e  amount of 
m u l t i s t e p  c o n t r i b u t i o n s  might be l a r g e r  than  a t  160 
MeV. Recent c a l c u l a t i o n s  by Esbensen and Ber tsch7 have 
poin ted  ou t  t h e  pos s ib l e  importance of mu l t i p l e  
s c a t t e r i n g  even a t  200 MeV. Note, however, t h a t  
randomization of t h e  neut ron  s p i n ,  a s  might be expected 
from a  simple mu l t i p l e  s c a t t e r i n g  model, would r e s u l t  
i n  Dm = 0. I f  t h i s  e f f e c t  i s  indeed impor tant ,  then  
comparison of Dm measurements t o  t h e o r e t i c a l  DWIA 
p r e d i c t i o n s  w i l l  be v a l i d  f o r  spec t ro scop ic  purposes 
only  f o r  t h e  h i g h e s t  bombarding energy. 
The observed r eg ion  of p o s i t i v e  Dm nea r  
Ex 40 MeV i n  t h e  120-MeV spectrum must s t i l l  be 
exp l a ined ,  e s p e c i a l l y  s i n c e  p o s i t i v e  Dm i s  t h e  
s i g n a t u r e  f o r  AS = 0 i n  a  s i n g l e  s t e p  t r a n s i t i o n  and 
such t r a n s i t i o n s  should  be enhanced a t  t h e  lower 
bombarding energy r e l a t i v e  t o  AS = 1 t r a n s i t i o n s .  
'present address :  Los Alamos Nat l .  Lab, P2 D iv i s ion ,  
Los Alamos, NM 87545 
1 )  T.N. Taddeucci e t  a l . ,  Phys. Rev. L e t t .  52,1960 
(1984). 
2 )  T.N. Taddeucci e t  a l . ,  Phys. Rev. C ( i n  p r e s s ) .  
3 )  C.D. Goodman e t  a l . ,  Phys. Rev. L e t t .  54, 877 
(1985). 
4 )  T.N. Taddeucci e t  a l . ,  Nucl. I n s t r .  and Meth. 
A241, 448 (1985).  
-
5 )  I?. O s t e r f e l d ,  D. Cha, and J. Speth,  Phys. Rev. C 
31, 372 (1985). 
-
6 )  W.A. S t e r r enbu rg ,  Sam M. Aust in ,  R.P. DeVito, and 
Aaron Galonsky, Phys. Rev. L e t t .  45, 1839 (1980). 
7 )  H. Esbensen and G.F. Ber tsch ,  Phys. Rev. C 32 
533 (1985). 
STRETCHED STATE EXCITATIONS I N  THE 2 6 ~ g ( p , n ) 2 6 ~ 1  REACTION AT 134 MeV 
B.D. Anderson, C. Lebo, T. C h i t t r a k a r n ,  A.R. Baldwin, J.W. Watson, and R. Madey 
Kent S t a t e  Un ive r s i t y ,  Kent, Ohio 44242 
C.C. F o s t e r  
I nd i ana  Un ive r s i t y  Cyclo t ron  F a c i l i t y ,  Bloomington, Indiana  47405 
For a  t a r g e t  wi th  a  neut ron  excess ,  t he  (p ,n)  
r e a c t i o n  (with AT = 1 )  can e x c i t e  s t r e n g t h  i n  t h e  f i n a l  
nucleus  wi th  i s o s p i n  T - 1, T, o r  T  + 1, where T is the  
i s o s p i n  of t he  t a r g e t .  By c o n t r a s t ,  i n e l a s t i c  e l e c t r o n  
and proton  s c a t t e r i n g  a r e  r e s t r i c t e d  t o  t h e  two h ighes t  
i s o s p i n  components. Because t h e  lower i s o s p i n  
component is u s u a l l y  found a t  lower e x c i t a t i o n  
ene rg i e s ,  it u s u a l l y  is fragmented l e s s  by 
c o n f i g u r a t i o n  mixing. The '0 6 w 1  s t r e t c h e d  s t a t e s  
observed i n  t h e  (p ,n )  r eac t i on1  a r e  good examples of 
T  - 1 s t r e t c h e d  s t a t e s .  I n  some ca se s ,  u s u a l l y  f o r  
l i g h t e r  n u c l e i ,  it is pos s ib l e  a l s o  t o  s ee  T - 1 
components of '1 6 w 1  s t r e t c h e d  s t a t e s ;  t h e  
2 6 ~ g ( p , n ) 2 6 ~ 1  r e a c t i o n  i s  a  good example. Because 2 6 ~ g  
is  a  T = 1 nucleus ,  t h e  (p ,n )  r e a c t i o n  can e x c i t e  
T  = 0, 1, and 2  i s o s p i n  components i n  t h e  2 6 ~ 1  r e s i d u a l  
nucleus .  The (p,p') and (e,e ' )  i n e l a s t i c  s c a t t e r i n g  
r e a c t i o n s  (wi th  both AT = 1 and AT = O), can e x c i t e  
only  s t a t e s  i n  2 6 ~ g ,  which has T, = 1; thus ,  t h e s e  
r e a c t i o n s  e x c i t e  only  T = 1 and T = 2 components i n  t h e  
f i n a l  nucleus.  Both t he  (p,p') and ( e , e M )  reaction^^,^ 
have been used t o  s tudy t h e  i s o v e c t o r  6' s t r e t c h e d  


Spin Transfer Measurements for (p,n) Reactions at Intermediate Energy

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Spin Transfer Measurements for (p,n) Reactions at Intermediate Energy

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